1. Field of the Invention
The invention relates in general to the measurement of flow velocity and, in particular, to an adjustable level and alignment bar for use with a top-setting wading rod to aid a hydrographer in maintaining the wading rod plumb and in alignment with the cross-section of a river or stream being measured.
2. Description of the Related Art
When studying wadable streams and rivers, flow measurements are often made using a tagline across the stream or river to measure width, a top-setting wading rod to measure depth, and a current meter (such as a mechanical velocity meter or an acoustic velocity meter) attached to the wading rod to measure flow velocity.
Referring to FIG. 1, a top-setting wading rod 10 typically includes a base 12, a stationary hexagonal rod 14, an adjustable current meter positioning rod 16, and a sliding support assembly 18 to which the current meter (not shown) is attached. The hexagonal rod 14 (also referred to as a “depth rod”) attaches to the base 12 and is graduated in 0.1-ft intervals for measuring depth. The sliding support assembly 18 is attached to the lower end of the meter positioning rod 16 and slides up and down the hexagonal rod 14.
The position of the current meter is set by raising or lowering the meter positioning rod 16. The meter-positioning rod 16 is graduated in 1-ft increments. A handle 20 at the top of the hexagonal rod is graduated in 0.1 ft increments. By aligning the marks on the handle 20 with the marks on the meter positioning rod 16 to read the depth, the current meter will be placed at a vertical distance 60% from the surface of the water. For example, if the depth is 2.4 ft, the 2-ft mark on the meter positioning rod 16 is aligned with the mark on the handle 20 representing 0.4 ft. In this position, the current meter will be centered 60% down from the surface of the water. The current meter can be placed at other depth levels (typically 0.2, 0.6, or 0.8 tenths of the depth), as desired or required by the particular situation.
In operation, the tagline (not shown) is positioned perpendicular to the current flow. A hydrographer places the base 12 of the wading rod 10 on the floor of the river or stream next to the tagline and reads the depth using the gradations on the hexagonal rod 14. The hydrographer sets the current meter at a desired level for measuring flow by adjusting the meter positioning rod 16. The current meter is positioned in the water so that it faces directly into the current. The current meter generates a signal proportional to flow velocity. The signal is transmitted through the wading rod 10 to a display (not shown).
When the hydrographer stands in the river or stream, it is difficult to determine whether the wading rod is held plumb due to the disorientation caused by the water flowing around the person making the measurement. Current meters are rated for a perfectly horizontal plane in a testing tank. The hydrographer can position the wading rod too far up or down the stream so that the current meter is out of vertical alignment or at an angle to the current flow. Thus, when the wading rod is not kept plumb and in alignment, the performance and accuracy of the current meter is adversely affected.
Bubble levels (not shown) have been used to help hold the wading rod 10 plumb by being taped or glued or otherwise securely fastened to the wading rod at a specific point, such as on the handle 20. This approach is not satisfactory because it assumes the hydrographer is at the same viewing level as the bubble level. If the wading rod needs to be placed on a rock or boulder for the next measurement, the hydrographer may not be able to see the level to keep the wading rod plumb and aligned. Also, the handle 20 of the top-setting wading rod 10, in practice, is not always in alignment with the hexagonal rod 14. The current meter slides up and down the hexagonal rod 14 and is in perpendicular alignment with it, not the handle 20.
Thus, there is a need for a level that can be easily attached to the wading rod and easily repositioned to make holding the wading rod plumb a simple task.